1. Field of the Invention
The invention relates to a hydrophobicizing, water-redispersible additive based on fatty acids and their derivatives and, where appropriate, organosilicon compounds, to a process for their preparation, and to their use.
2. Description of the Related Art
Lime- or cement-bound construction materials, such as renders, trowelling compounds and construction adhesives need protection from the effects of weathering. Rain or snow causes wetting throughout the construction materials, for example the external render, as a result of capillary action, and this can lead to irreversible damage to the building. Hydrophobicization of the construction materials is a familiar and longstanding method of preventing this.
DE-A 2341085, EP-A 342609 and EP-A 717016 disclose that fatty acid esters may be added as hydrophobicizing agents to lime- or cement-bound renders. A frequent disadvantage here is specifically the hydrophobicizing character of these additives. If dry renders in which these hydrophobicizing agents are present are mixed with water the result is then poor wetting of the materials, and therefore markedly impaired processability.
Water-redispersible powders based on homo- or copolymers of ethylenically unsaturated monomers are used in the construction sector as binders, in combination with hydraulically setting binders, such as cement. By way of example, these are used in construction adhesives, renders, mortars, and paints to improve mechanical strength and adhesion. WO-A 95/20627, WO-A 02/31036 and DE-A 10233933 disclose that additives with hydrophobicizing action, such as organosilicon compounds and fatty acid esters, may be used as a constituent of redispersion powders in dry mortars. The problems of poor wettability and processability are thus circumvented. However, the hydrophobicizing effect is dependent on the proportion of the hydrophobicizing agent in the redispersion powder and cannot therefore be varied as desired.
EP-A 1193287 recommends powder compositions with at least one fatty acid ester for hydrophobicizing construction material compositions. To this end, the fatty acid ester is applied as described immediately above as a constituent of a redispersible polymer powder, with precisely the disadvantages described. Another embodiment proposes using the hydrophobicizing agent as dry substance, applied to an inert, inorganic carrier material, such as silica. A disadvantage here is that an inert substance is therefore introduced into the construction material composition, and this can have an adverse effect on its mechanical strength.